Chewy,
Firstly I suggest a search within these hallowed walls for the information you want - it's all there.
Secondly, for the US a visa is a must - waivers and tourist visas are not acceptable for flight training.
Thirdly, why go for an FAA licence if you're going to be flying in the UK? Get a JAR licence in the US at an approved school. You'd have more trouble converting to a JAR licence in the UK. FAA licences are perfectly acceptable here, but the paperwork and possible suspicion that clubs may treat you is not worth the hassle. Search for a few Florida JAA approved schools in PF - there's plenty of them. Both ways will require some hours familiarisation when back in the UK.
Finally, why July? Apparently the weather is better (less thermal activity etc) in November/January.
Remember these are all my personal opinions, best thing is to look at all the options - Spain, South Africa, Cananda etc.
Confab